1. Field of the Invention
This invention relates generally to an apparatus and a method for guiding an electric discharge and in particular, to a laser guided discharge device which is capable of guiding a discharge current between two electrodes wherein laser light and an external magnetic field provide a guiding wall.
2. Description of Related Art
Traditionally, "wall-guided" gas discharge tubes have been used in lasers, flashlamps, etc . . . Such a discharge tube guides an electric discharge in a gas between two electrodes using the inner wall of the tube containing the gas. In order to avoid shorting out the electric discharge, the inner wall of such a tube must be made of electrically insulating materials such as glass or ceramic. In addition, in order to prevent corrosion and consequently prolong the life of the tube, the inner wall of the tube must be made of materials which do not chemically react with the gas.
The above two requirements place severe limitations on the types of materials which can be used to make discharge tubes. For example, metals such as steel, tungsten and nickel cannot be used to guide an electric discharge between electrodes in "wall-guided" discharge tubes, because although they possess particular advantages for housing gases such as high impact resistance, longevity and design flexibility, they are not electrically insulating. Also, if the gas is a metal vapor such as an alkali (group IA of the periodic table), alkaline earth metals (group IIA of the periodic table) or some other transition element (groups IIIA to VIIIA, IB and IIB), a non-metallic tube cannot be used to guide the electric discharge, because eventually, atoms in the gas will accumulate on the inner walls of the tube and chemically or physically attack those inner walls. This can result in shorting out or destroying the walls of the tubes as well as and other components of the device.
Very high powered lasers such as carbon dioxide lasers of several hundred megawatts can be used to direct or guide lightening bolts, see, for example, "Lightening Lure", page 105, Scientific American, Feb. 1993. However, such high powered lasers are expensive, dangerous and can only guide lighting bolts a short distance (e.g. about 10 meters).
Laser guided discharge (LGD) devices such as those disclosed in U.S. Application Ser. No. 07/926,294 alleviate the above problems by guiding an electric discharge in a material without using a guiding tube. LGD devices can also guide electric discharge devices in materials that are intrinsically incompatible (chemically or physically) such as metal vapors with present day wall materials. LGD devices accomplish this by using laser photons tuned to an electronic quasi-resonance of the material, thus creating and sustaining a channel that guides the electric discharge between the electrodes.
LGD devices are capable of operating under high power conditions, i.e., conditions where a power supply across the electrodes of the LGD device is over several hundred watts. Such a high power LGD device typically requires a housing made of metal to withstand high pressures and typically operates under high power, high pressure, high current and high voltage conditions. Such metal housings, however, produce significant "wall losses", i.e. losses due to the presence of electric currents in the walls of the housing.